EER Flashcards
what is an Nary relationship
has more than two entities participating. Required when a binary relationship is not sufficient
what do enhanced models include that normal models do not
inheritance
category and union types
specialisation and generalisation
super and subclasses
what are the benefits of an enhanced relationship diagram
more accurate to schema
reflects properties more precisely
expresses more
describe sub and super classes
a superclass has one or more subtypes
subclasses have unique attributes and inherits properties and attributes from superclass
describe specialisation
top down- set to subset
can be separated in diagram
increases size of schema
describe generalisation
bottom up- subset to set
reduces size of schema
if there is a higher entity, there must be a lower
what is disjoint
each is only one
what is overlap
each can be one or more
what is union
each can be one or more
subclass has own key
